Break CO2 emissions into population, GDP per person, energy intensity and carbon intensity with the Kaya identity — all figures are estimates, as the factors vary by country and year.
Estimates only: energy and carbon intensities vary by country, year and energy mix. This is an accounting identity, not a forecast.
Annual CO2 (Gt)
How to use this tool
Type the population, GDP per person, energy intensity and carbon intensity. The defaults are rough global averages, not any single country.
The headline result is annual CO2 in gigatonnes, with total GDP and energy alongside it.
Halve the carbon intensity, for example, and watch total emissions halve — that is the point of the decomposition.
Try a richer, cleaner or more efficient world and compare totals; treat every figure as an estimate.
Formula & worked example
With 8 billion people, $12,000 GDP per person, 5 MJ per dollar and 50 g CO2 per MJ, the identity gives 24 Gt of CO2 per year — about 3 tonnes per person.
Limitations — read this before you rely on it
The Kaya identity is an accounting decomposition, not a forecast: it shows which factor must fall for emissions to fall, but it does not predict how any factor will move, and national factors differ widely from the global averages used as defaults.
Frequently asked questions
It is a way of writing total CO2 emissions as the product of four factors: population, affluence (GDP per person), energy intensity and carbon intensity. If one factor doubles and the rest stay fixed, emissions double.
Because total GDP is population times GDP per person, total energy is GDP times energy per dollar, and total CO2 is energy times CO2 per unit of energy. Cancelling terms leaves CO2.
Yes, if energy intensity or carbon intensity falls faster than GDP grows. That is the whole decarbonisation challenge in one equation.
No. They are rough global averages for illustration. Enter your own country or scenario factors for a meaningful result.
No. The Kaya identity as used here covers energy-related CO2 only, not methane, land use or other gases.